Pliable sheets of thermoplastic materials are commonly used in many industrial and civil construction applications. For instance a single ply form is utilized as a roof membrane to prevent leakage of water through a roof. Additionally, such sheets of thermoplastic materials are also used as pond liners to contain hazardous wastes and to prevent such wastes from seeping into the ground. Typically, in such applications, large sheets of thermoplastic materials are placed on the roof or into a containment pond in an overlapping relationship and then welded to one another along the overlap. This is done manually with an artisan separating the sheets along the overlap, applying heat by a hot air heating element between the separation and then using a roller to press the sheets back into contact with one another to provide a weld. As can be appreciated, such manual welding techniques are very time consuming and therefore expensive. Moreover, the weld produced is not uniform and thus leakage sometimes occurs within the weld itself. The present invention therefore, seeks to automate this welding process to decrease the time involved in such construction as well as to insure that a uniform weld is produced at the overlap of the materials. Moreover, the welding can take place outdoors, over rough terrain, and therefore, it can be very difficult for an artisan, in the first instance, to produce a weld between materials.